Laser processing method and laser processing apparatus

ABSTRACT

A laser processing method for laser processing of a workpiece made of a base material and a fiber reinforced composite material containing fibers having a thermal conductivity and a processing threshold higher than physical properties of glass fibers. The laser processing method includes a step of processing the workpiece by forming a plurality of through-holes extending through the workpiece by irradiating the workpiece with pulsed laser light from a processing head while relatively moving the workpiece and the processing head in a predetermined cutting direction. The pulsed laser light has a pulse width smaller than 1 ms and an energy density capable of forming each of the through-holes by a single pulse.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based on PCT filing PCT/JP2018/044411, filedDec. 3, 2018, the entire contents of which are incorporated herein byreference.

FIELD

The present invention relates to a laser processing method and a laserprocessing apparatus for cutting a workpiece by emitting laser light tothe workpiece.

BACKGROUND

Fiber reinforced composite materials, such as glass fiber reinforcedplastics (GFRP), composed of a base material and reinforcing fibers haverecently attracted attention as strong and lightweight materials.Because the base material and the reinforcing fibers have differentcharacteristics from each other, the fiber reinforced compositematerials are known to be difficult to process. A laser processingapparatus can increase the processing speed by increasing a laseroutput, and may therefore be used for processing a fiber reinforcedcomposite material when a high processing speed is required.

Patent Literature 1 describes forming a plurality of through-holes eachformed by a single pulse of pulsed laser, and making through-holesadjacent to each other partly overlap each other, to cut a glass fiberreinforced resin film.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent Application Laid-open No.    2011-098381

SUMMARY Technical Problem

Patent Literature 1, however, does not mention cutting of a fiberreinforced composite material containing fibers having physicalproperties of processing threshold and thermal conductivity that aresignificantly higher than those of GFRP.

For example, a carbon fiber reinforced plastic (CFRP) is composed of twotypes of materials, which are carbon fibers and resin, having thermalproperties that are significantly different from each other, and thecarbon fibers having a thermal conductivity higher than that of theresin act as a transfer path of heat generated during laser processing.In the CFRP, the carbon fibers has a melting point of about 3500° C.,and the resin has a melting point of about 250° C. In this case, thetemperature at a processing point during cutting is adjusted to thehigher melting point, that is, to 3500° C. or higher. There is thereforea concern that, during laser processing of a CFRP, thermal damage causedduring processing spreads to resin around a processed portion owing toheat transferred from carbon fibers. Thus, in cutting of the CFRP, it isdesirable that one hole be made to penetrate the CFRP by a single pulseof pulsed laser in order to reduce thermal effects on the resin.

In the CFRP, when the adhesion at an interface between a fiber surfaceand the resin is lowered by thermal damage, the mechanical strengthproperties of the CFRP as a structural material are degraded, and thequality of the cut CFRP is lowered. Thus, in processing of the CFRP,spread of thermal damage to the vicinity of a processing point needs tobe avoided as possible.

The present invention has been made in view of the above, and an objectthereof is to provide a laser processing method capable of processing afiber reinforced composite material with reduced thermal effect on resinin the fiber reinforced composite material.

Solution to Problem

To solve the aforementioned problems and achieve the object, a laserprocessing method according to the present invention is a processingmethod for laser processing of a workpiece made of a base material and afiber reinforced composite material, the fiber reinforced compositematerial containing fibers having a thermal conductivity and aprocessing threshold higher than physical properties of glass fibers.The laser processing method includes a step of processing the workpieceby forming a plurality of through-holes extending through the workpieceby irradiating the workpiece with pulsed laser light from a processinghead while relatively moving the workpiece and the processing head in apredetermined cutting direction. The pulsed laser light has a pulsewidth smaller than 1 ms and an energy density capable of forming each ofthe through-holes by a single pulse.

Advantageous Effects of Invention

A laser processing method according to the present invention produces aneffect of enabling processing of a fiber reinforced composite materialwith reduced thermal effect on resin in the fiber reinforced compositematerial.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating a functional configuration of a laserprocessing apparatus according to a first embodiment of the presentinvention.

FIG. 2 is a schematic view illustrating an example of a hardwareconfiguration of the laser processing apparatus illustrated in FIG. 1 .

FIG. 3 is a drawing illustrating a laser processing method used by thelaser processing apparatus illustrated in FIG. 1 .

FIG. 4 is a table illustrating physical properties of a CFRP.

FIG. 5 is a graph illustrating an output waveform of a pulsed laser,which is pulsed laser light, output in the laser processing apparatusillustrated in FIG. 1 , the graph illustrating the output waveform ofthe pulsed laser having energy capable of forming a processing hole,which is a through-hole extending through a workpiece in the thicknessdirection, by a single irradiation.

FIG. 6 is a schematic view illustrating a processing state when theprocessing conditions of processing of a workpiece with the pulsed laserlight do not meet the condition of formula (3), and specifically, whenan overlap ratio is smaller than 0.

FIG. 7 is a schematic view illustrating a processing state when theprocessing conditions of processing of the workpiece with the pulsedlaser light meet the condition of formula (3).

FIG. 8 is a schematic view illustrating a processing state when theprocessing conditions of processing of a workpiece with the pulsed laserlight do not meet the condition of formula (3), and specifically, whenthe overlap ratio is equal to or larger than 0.5.

FIG. 9 is a schematic cross-sectional view illustrating a stateimmediately after a first irradiation of a processing point of theworkpiece with the pulsed laser light.

FIG. 10 is a schematic cross-sectional view illustrating a state duringa period for which a bottom part of a hole is let stand after the firstirradiation of the processing point of the workpiece with the pulsedlaser light.

FIG. 11 is a schematic cross-sectional view illustrating a stateimmediately after a second irradiation of the processing point of theworkpiece with the pulsed laser light.

FIG. 12 is a schematic cross-sectional view illustrating a state duringa period for which the bottom part of the hole is let stand after thesecond irradiation of the processing point of the workpiece with thepulsed laser light.

FIG. 13 is a schematic cross-sectional view illustrating a state afterthe processing point of the workpiece is irradiated with the pulsedlaser light a plurality of times and a through-hole is thus formedthrough the workpiece.

FIG. 14 is a graph illustrating an output waveform of a CW laser in acase where cutting is performed by the CW laser at the same processingspeed as the pulsed laser having the output waveform illustrated in FIG.5 .

FIG. 15 is a diagram illustrating an example in which a nozzle, which isa side flow nozzle for emitting a jet of gas from outside of an opticalaxis toward the optical axis, is used.

FIG. 16 is a diagram illustrating an example in which an axial nozzlefor emitting a jet of gas from a direction along the optical axis towarda processing point is used.

FIG. 17 is a table illustrating an example of cutting conditions withwhich a good processing quality of a workpiece was obtained by cuttingusing the laser processing apparatus.

FIG. 18 illustrates an image of a processing sample cut by the cuttingusing the laser processing apparatus.

FIG. 19 illustrates an enlarged image of a region A of the processingsample illustrated in FIG. 18 .

FIG. 20 is a diagram illustrating a laser processing method for cuttinga cut length by performing scanning with the pulsed laser light twice inthe laser processing apparatus illustrated in FIG. 1 , in which a stateof first scanning with the pulsed laser light is illustrated.

FIG. 21 is a diagram illustrating the laser processing method forcutting the cut length by performing scanning with the pulsed laserlight twice in the laser processing apparatus illustrated in FIG. 1 , inwhich a state of second scanning with the pulsed laser light isillustrated.

FIG. 22 is a diagram illustrating a hardware configuration forimplementing the functions of a control unit illustrated in FIG. 1 .

DESCRIPTION OF EMBODIMENTS

A laser processing method and a laser processing apparatus according tocertain embodiments of the present invention will be described in detailbelow with reference to the drawings. Note that the present invention isnot limited to the embodiments.

First Embodiment

FIG. 1 is a diagram illustrating a functional configuration of a laserprocessing apparatus 100 according to a first embodiment of the presentinvention. FIG. 2 is a schematic view illustrating an example of ahardware configuration of the laser processing apparatus 100 illustratedin FIG. 1 . FIG. 3 is a drawing illustrating a laser processing methodused by the laser processing apparatus 100 illustrated in FIG. 1 . FIG.3 illustrates main part relating to laser processing performed by thelaser processing apparatus 100. The laser processing apparatus 100includes a laser oscillator 11, an optical path 12, a processing head13, a driving unit 14, a nozzle 15, a nozzle moving mechanism 16, adetecting unit 17, and a control unit 18.

The laser processing apparatus 100 has a function of irradiating aworkpiece W with pulsed laser light 1 to cut the workpiece W. Theworkpiece W in the first embodiment is a plate-like workpiece made of afiber reinforced composite material including a base material andreinforcing fibers. An example of the fiber reinforced compositematerial is a CFRP. The CFRP is a workpiece made of a fiber reinforcedcomposite material including a base material and a fiber having a higherthermal conductivity and a higher processing threshold than physicalproperties of a glass fiber.

FIG. 4 is a table illustrating physical properties of the CFRP. In theCFRP, the reinforcing fibers are carbon fibers having a diameter in arange of equal to or larger than 5 micrometers and equal to or smallerthan 10 micrometers. In the workpiece W, a plurality of reinforcingfibers are arranged along a predetermined direction. In FIG. 3 , thepredetermined direction is a direction from the bottom left toward thetop right of the drawing.

The base material is a thermosetting resin typified by epoxy resin. Thecarbon fibers have a thermal conductivity in a range of equal to orhigher than 100 W/m·K and equal to or lower than 800 W/m·K, which ishigher than the thermal conductivity of the resin that is 0.3 W/m·K. Thecarbon fibers have a melting point in a range of equal to or higher than2000° C. and equal to or lower than 3500° C., which is higher themelting point of the resin that is equal to or lower than 250° C. Thus,the carbon fibers and the resin in the CFRP have melting points andthermal conductivities that are significantly different from each other;the carbon fibers are significantly higher than the base material inboth of the properties. Thus, the CFRP, which is an example of the fiberreinforced composite material is a composite material including the basematerial and the carbon fibers having a thermal conductivity and aprocessing threshold that are higher than those of the base material.

The workpiece W made of the CFRP includes carbon fibers Wa, which arereinforcing fibers, and a resin Wb, which is the base material. WhileFIG. 2 , etc. illustrate a state in which a plurality of carbon fibersWa are arranged in a plurality of layers in the resin Wb for convenienceof illustration, more carbon fibers Wa are arranged in the predetermineddirection in the resin Wb in practice. Assume that the surface of theworkpiece W is on an XY plane and the direction perpendicular to the XYplane is a Z-axis direction. The emitting direction of the pulsed laserlight 1 is parallel to the Z axis.

For comparison, the physical properties of the GFRP that is a workpiecein Patent Literature 1 are also illustrated in FIG. 4 . FIG. 4 showsthat the CFRP has a processing threshold and a thermal conductivity thatare both significantly higher than those of the GFRP. Note that the highthermal conductivity of the carbon fibers means a high concern thatthermal damage spreads to resin around a processed portion owing to heattransferred from carbon fibers during laser processing. The high meltingpoint of the carbon fibers means that the carbon fibers are hard toprocess. Thus, the high melting point of the carbon fibers means thatthe carbon fibers have a high processing threshold and are hard toprocess. The processing threshold refers to a minimum energy density ofthe pulsed laser light 1 when the workpiece being irradiated with thepulsed laser light 1 starts to decompose.

The laser oscillator 11 oscillates and emits the pulsed laser light 1.The laser oscillator 11 used in the laser processing apparatus 100according to the first embodiment is preferably a CO₂ laser oscillator.Thus, the pulsed laser light 1 used in the laser processing apparatus100 according to the first embodiment is preferably a CO₂ laser light.

The pulsed laser light 1 emitted by the laser oscillator 11 is suppliedto the processing head 13 via the optical path 12. The optical path 12is a path for transmitting the pulsed laser light 1 emitted by the laseroscillator 11 to the processing head 13, and may be a path forpropagating the pulsed laser light 1 in air or a path for transmittingthe pulsed laser light 1 through an optical fiber. The optical path 12is designed depending on the characteristics of the pulsed laser light1.

The processing head 13 includes an optical system for focusing thepulsed laser light 1 onto the workpiece W. The processing head 13collects the supplied pulsed laser light 1 and irradiates one surface ofthe workpiece W, which is a surface to be processed, with the pulsedlaser light 1. The processing head 13 desirably includes an opticalsystem that focuses near the surface of the workpiece W.

The driving unit 14 can perform control to change relative positions ofthe processing head 13 and the workpiece W. While the driving unit 14changes the relative positions of the processing head 13 and theworkpiece W by changing the position of the processing head 13 in thelaser processing apparatus 100, the driving unit 14 may alternativelychange the position of a table on which the workpiece W is placed or thepositions of both of the processing head 13 and the table on which theworkpiece W is placed. Thus, the driving unit 14 may include a functionof changing the position of at least one of the processing head 13 andthe workpiece W.

The cutting of the workpiece W is performed by the processing head 13 byirradiating the workpiece W with the pulsed laser light 1 while thedriving unit 14 changes the relative positions of the processing head 13and the workpiece W.

The nozzle 15 is a gas jet nozzle for emitting a jet of gas 23 to aportion of the workpiece W irradiated with the pulsed laser light 1 fromthe processing head 13. The nozzle 15 emits the jet of gas 23 fromoutside of the optical axis 1 a of the pulsed laser light 1, which isemitted from the processing head 13 to the workpiece W, toward theoptical axis 1 a. More specifically, the nozzle 15 emits a jet of gas 23from outside of the optical axis 1 a of the pulsed laser light 1, whichis emitted from the processing head 13 to the workpiece W, toward aprocessing point on the workpiece W being processed by the pulsed laserlight 1. The position of the nozzle 15 is changed by the nozzle movingmechanism 16. The position of the nozzle 15 can be moved to any positionby the control of the control unit 18 during the processing of theworkpiece W.

The detecting unit 17 is a sensor for detecting the state of theworkpiece W or the state of the laser processing apparatus 100. Thedetecting unit 17 measures, as time-series signals, the position of theworkpiece W being processed and measured values of physical quantitiessuch as the intensity and the wavelength of light, sound waves, andultrasonic waves generated during the processing. The detecting unit 17is a capacitive sensor, a photodiode, a charge coupled device (CCD)sensor, a complementary metal oxide semiconductor (CMOS) sensor, aspectroscope, an acoustic sensor, an acceleration sensor, a gyro sensor,a distance sensor, a position detector, a temperature sensor, a humiditysensor, or the like, for example. The detecting unit 17 inputstime-series signals indicating the measured values to the control unit18.

The control unit 18 controls the laser oscillator 11, the driving unit14, the nozzle moving mechanism 16, and the like so that the pulsedlaser light 1 scans a processing path on the workpiece W in accordancewith set processing conditions and the measured values transmitted fromthe detecting unit 17. The processing conditions include the materials,the thickness, and the surface state of the workpiece W, for example.The processing conditions further include the laser output intensity,the laser output frequency, and the duty cycle, the mode, the waveform,and the wavelength of laser output of the laser oscillator 11, and thelike. The processing conditions can include the focal position of thepulsed laser light 1, the focus diameter of the pulsed laser light 1,the type and the pressure of gas emitted from the nozzle 15, the holediameter of the nozzle, the processing speed, and the like. In addition,the processing conditions can also include the measured values inputfrom the detecting unit 17 such as the distance between the workpiece Wand the processing head 13, temperature, and humidity.

An optical unit 22 including a condenser lens 21 for focusing the pulsedlaser light 1 onto a processing point is part of the processing head 13illustrated in FIG. 1 .

The laser processing apparatus 100 performs cutting, in which onesurface of the workpiece W is irradiated with the pulsed laser light 1to separate the workpiece W into a processed product 29 and an offcut28. The processed product 29 is to be used as a part or the like aftercutting, and the offcut 28 is to be waste after cutting. The position onthe workpiece W to be irradiated with the pulsed laser light 1 iscontrolled to be moved along the processing path by the control unit 18.

Next, a method for processing a CFRP, which is the workpiece W, by thelaser processing apparatus 100 will be explained. For cutting of theworkpiece W, the pulsed laser light 1 is focused onto the surface of theworkpiece W by the condenser lens 21 as illustrated in FIG. 3 . Thesurface to be processed of the workpiece W is irradiated with the pulsedlaser light 1 by being scanned along a predetermined cutting direction.Specifically, the relative positions of the processing head 13 and theworkpiece W are changed to change the position on the workpiece Wirradiated with the pulsed laser light 1.

FIG. 5 is a graph illustrating an output waveform of a pulsed laser,which is the pulsed laser light 1, output in the laser processingapparatus 100 illustrated in FIG. 1 , the graph illustrating the outputwaveform of the pulsed laser having energy capable of forming aprocessing hole 41, which is a through-hole extending through theworkpiece W in the thickness direction, by a single irradiation. Thenumber of pulses of the pulsed laser light 1 with which the workpiece Wis irradiated to cut the workpiece W by a cut length L is represented byN. N is a positive number equal to or larger than 2. For example, whenthe workpiece W is cut by a single scanning by repeating irradiationwith the pulsed laser at a frequency f as illustrated in FIG. 5 whilemoving the irradiation position of the pulsed laser light 1 at ascanning rate v, the number N of pulses of the pulsed laser light 1 withwhich the workpiece W is irradiated is expressed by the followingformula (1).N=L×f/v  (1)

When the diameter of the processing hole 41 processed with a singlepulse of the pulsed laser light 1 in the cutting direction of theworkpiece W is represented by a processing hole diameter d, an overlapratio ro in the cutting direction of two processing holes that areadjacent to each other in the cutting direction, that is, the overlap ofthe processing holes in the cutting direction is expressed by formula(2) below. The cutting direction of the workpiece W is the same as thescanning direction of the pulsed laser light 1. The overlap ratio ro isa ratio of the length by which two processing holes that are adjacent toeach other in the cutting direction overlap each other in the cuttingdirection to the processing hole diameter d. The processing holediameter d is equal to the focus diameter of the pulsed laser light 1.In other words, the processing hole diameter d is the focus diameter dof the pulsed laser light 1 in the cutting direction of the workpiece W.Note that, in the drawings such as FIG. 3 , the processing hole diameterd is illustrated as being larger than the focus diameter of the pulsedlaser light 1 for ease of understanding of the overlapping state of theprocessing holes.ro=(d−L/N)/d  (2)

In addition, in the first embodiment, laser processing is performed withthe overlap ratio ro within a range of larger than 0 and smaller than0.5 as expressed by the following formula (3).0<ro=(d−L/N)/d<0.5  (3)

Next, the capability of cutting through the workpiece W by a singlepulse of pulsed laser light 1 emitted in such a manner as to meet thecondition of formula (3) above will be explained. FIGS. 6 to 8 areschematic views illustrating the states of the workpiece W processed bythe pulsed laser light 1 when the overlap ratio ro is changed. FIG. 6 isa schematic view illustrating a processing state when the processingconditions of processing of the workpiece W with the pulsed laser light1 do not meet the condition of formula (3), and specifically, when theoverlap ratio ro is smaller than 0. FIG. 7 is a schematic viewillustrating a processing state when the processing conditions ofprocessing of the workpiece W with the pulsed laser light 1 meet thecondition of formula (3). FIG. 8 is a schematic view illustrating aprocessing state when the processing conditions of processing of theworkpiece W with the pulsed laser light 1 do not meet the condition offormula (3), and specifically, when the overlap ratio ro is equal to orlarger than 0.5. In FIGS. 6 to 8 , the nozzle 15 is not illustrated.

As illustrated in FIG. 6 , the case where the processing conditions ofprocessing of the workpiece W with the pulsed laser light 1 do not meetthe condition of formula (3), and specifically, where the overlap ratioro is smaller than 0 means a case where the processing holes 41 that areadjacent to each other in the cutting direction do not overlap eachother in the cutting direction. Thus, the workpiece W cannot be cut bythe processing illustrated in FIG. 6 .

As illustrated in FIG. 8 , in the case where the processing conditionsof processing of the workpiece W with the pulsed laser light 1 do notmeet the condition of formula (3), and specifically, where the overlapratio ro is equal to or larger than 0.5 and the overlap of two adjacentprocessing holes 41 in the cutting direction is larger than thecondition of formula (3), the irradiation with the pulsed laser light 1is performed twice or more times over the entire cut length L. In thiscase, an excessive quantity of heat, which does not contribute tocutting, input to the workpiece W increases, causing an unnecessarythermal effect from the inner face of the processing hole 41 onto thesurrounding resin Wb. In addition, the number of times of irradiationwith the pulsed laser light 1 necessary for cutting the cut length Lincreases, and use of laser energy increases.

In contrast, the case illustrated in FIG. 7 is a case where theprocessing conditions of processing of the workpiece W with the pulsedlaser light 1 meet the condition of formula (3), and only energycorresponding to a single pulse of the pulsed laser light 1 is input toa dot-hatched processing region 42 within the cut length L in FIG. 7 .The capability of cutting the cut length L of the workpiece W in thisstate indicates that processing holes 41 extending through the workpieceW in the thickness direction are each formed with energy correspondingto a single pulse of the pulsed laser light 1 to perform cutting.

Specifically, in the case illustrated in FIG. 7 , within the region inwhich the processing holes are formed, the cut length L is cut in astate in which a region irradiated with the pulsed laser twice in thescanning direction of the pulsed laser light 1 is smaller than that inthe case illustrated in FIG. 8 . Specifically, in the case where theprocessing conditions of processing of the workpiece W by the pulsedlaser light 1 meet the condition of formula (3) as illustrated in FIG. 7, in the laser processing method of performing cutting by repeatingirradiation with a single pulsed laser while moving the pulsed laserlight 1, a processing hole 41, which is a through-hole extending throughthe workpiece W, is formed by a single irradiation with the pulse laserto cut the workpiece W. In this manner, the workpiece W can be cut witha reduced thermal effect on the resin Wb in the workpiece W.

Note that, in FIG. 7 , a processing hole 41 with a semicircular openingshape is formed by irradiation with the pulsed laser light 1 when n=0.In addition, a processing hole 41 with a circular opening shape isformed by irradiation with the pulsed laser light 1 when n=N. Note thatpart of the processing hole 41 formed when n=N that is necessary forcutting the cut length L is the part with a semicircular opening shapeadjacent to the processing hole 41 formed when n=N−1. Thus, acombination of the part having the semicircular opening shape of theprocessing hole 41 formed when n=0 and the part having the semicircularopening shape of the processing hole 41 formed when n=N can be regardedas one circular processing hole 41. Thus, in the case illustrated inFIG. 7 , the number of pulses of the pulsed laser light 1 with which theworkpiece W is irradiated to cut the cut length L of the workpiece W canbe assumed to be N.

For cutting of the workpiece W by the laser processing apparatus 100,the control unit 18 controls to change the relative positions of theprocessing head 13 and the workpiece W by controlling the driving unit14 to meet the condition of formula (3) above. Thus, for performingcutting of the workpiece W, the control unit 18 controls the relativepositions of the irradiation position of the pulsed laser light 1 andthe workpiece W to meet the condition of formula (3) above.

While the overlap ratio ro is in the range of “0<ro<0.5” as describedabove in the first embodiment, the overlap ratio ro is more preferablyas small as possible within the “0<ro<0.5”, that is, as close to 0 aspossible. When the overlap ratio ro is as small as possible, the pulsedlaser light 1 with which part of a through-hole that already extendsthrough the workpiece W is irradiated again can be reduced, and input ofexcessive heat, which does not contribute to cutting, to the workpiece Wcan be reduced.

An optimum value of the overlap ratio ro is 0.2. When the overlap ratioro is 0.2, the cutting speed is not decreased, and a cut end facebecomes smoother. Thus, when the overlap ratio ro is 0.2, decrease inthe processing speed can be prevented and higher smoothness of a cut endface can be achieved even with the processing holes 41 overlapping eachother.

The advantageous effects of cutting the workpiece W by forming a holethrough the workpiece W by a single irradiation of a pulsed laser by thelaser processing method for processing the workpiece W according to thefirst embodiment as described above will be explained in comparison witha laser processing method according to a comparative example in whichhole processing is repeated a plurality of times in the depth directionof the workpiece W to cut the workpiece W.

In the laser processing method of the comparative example explainedbelow, a through-hole that extends through the workpiece W is not formedby a single irradiation of the pulsed laser light 1, but a through-holethat extends through the workpiece W is formed by irradiating oneposition with the pulsed laser light 1 a plurality of times to cut theworkpiece W. FIG. 9 is a schematic cross-sectional view illustrating astate immediately after a first irradiation of a processing point of theworkpiece W with the pulsed laser light 1. FIG. 10 is a schematiccross-sectional view illustrating a state during a period for which abottom part 52 of a hole 51 is let stand after the first irradiation ofthe processing point of the workpiece W with the pulsed laser light 1.FIG. 11 is a schematic cross-sectional view illustrating a stateimmediately after a second irradiation of the processing point of theworkpiece W with the pulsed laser light 1. FIG. 12 is a schematiccross-sectional view illustrating a state during a period for which thebottom part 52 of the hole 51 is let stand after the second irradiationof the processing point of the workpiece W with the pulsed laser light1. FIG. 13 is a schematic cross-sectional view illustrating a stateafter the processing point of the workpiece W is irradiated with thepulsed laser light 1 a plurality of times and a through-hole is thusformed through the workpiece W. FIGS. 9 to 13 correspond to crosssections along line IX-IX, line X-X, line XI-XI, line XII-XII, and lineXIII-XIII, respectively, in FIG. 8 .

For ease of understanding, assume that the pulsed laser light 1 has atop-hat beam profile and that the workpiece W is processed in conformitywith the beam shape. At the bottom part 52 of the hole 51 formed byirradiation of the workpiece W with the pulsed laser light 1 immediatelyafter the first irradiation of the processing point of the workpiece Wwith pulsed laser light 1, carbon fibers Wa that remain at a hightemperature are present because input energy has not reached theprocessing threshold, that is, the temperature thereof has not reachedthe melting point.

The melting point of the carbon fibers Wa is about 3500° C. The carbonfibers Wa remain at a temperature close to 3500° C. without beingremoved. In addition, until the hole 51 is irradiated with next laserlight 1, the heat of the carbon fibers Wa remaining at a hightemperature at the bottom part 52 of the hole 51 is transferred to theresin Wb around the hole 51 through the carbon fibers Wa, which have athermal conductivity significantly higher than that of the resin, and aheat-affected zone 53 is thus formed. The heat of the carbon fibers Wais transferred downward beneath the hole 51 and in outward directionsaway from the hole 51 as indicated by arrows in FIG. 10 .

The heat-affected zone 53 is a region of the resin Wb affected by heatresulting from a temperature increase by the heat of carbon fibers Wa,which remain at a high temperature at the bottom part 52 of the hole 51,the heat being transferred through the carbon fibers Wa. The heattransfer of the heat of the carbon fibers Wa, which remain at a hightemperature at the bottom part 52 of the hole 51, through the carbonfibers Wa is generated after the first irradiation with the pulsed laserlight 1 and before the second irradiation with the pulsed laser light 1,during a let-stand period for which the high-temperature carbon fibersWa at the bottom part 52 of the hole 51 are let stand.

The quantity of heat transferred from the carbon fibers Wa to the resinWb during this period is a large heat quantity for the resin, which is abase material having a melting point of 250° C. or lower and a lowprocessing threshold. Assume that the heat of the carbon fibers having atemperature of about 3500° C. and a length of a hole diameter d1 at thebottom part 52 of the hole 51 is transferred to the resin Wb through thecarbon fiber Wa. In this case, a length D of a range in which the resinWb, which is the base material, reaches the processing threshold in theextending direction of the carbon fibers Wa is expressed by formula (4)below and, which is 14 times the hole diameter d1 of the bottom part 52.The range length D corresponds to a range with its center as the centralaxis of the hole 51 in the extending direction of the carbon fibers Wa.D=d1×3500/250=14×d1  (4)

When the hole diameter d1 is 0.2 mm, D becomes 2.8 mm, and the length hof the heat-affected zone 53 in the extending direction of the carbonfibers Wa is h=2.8/2−0.2/2=1.3 mm, which is significantly larger thanthe hole diameter d1. The length h of the heat-affected zone 53 is alength in the extending direction of the carbon fibers Wa from an openend of the hole 51 to an outer end of the heat-affected zone 53 in theextending direction of the carbon fibers Wa.

In the heat-affected zone 53, the adhesion at the interfaces between thecarbon fibers Wa and the resin Wb is lowered by thermal damage, themechanical strength properties of the workpiece W as a structuralmaterial are degraded, and the quality of the cut workpiece W islowered, the degree of which varies depending on the energy of thepulsed laser light 1.

Subsequently, when a cutting position of the workpiece W where the hole51 is formed is irradiated with the pulsed laser light 1 for the secondtime, the hole 51 becomes deeper, and another heat-affected zone 53 thatexpands downward and outward from the heat-affected zone 53 formed bythe first irradiation with the pulsed laser light 1 is formed during alet-stand period until next irradiation with the pulsed laser light 1 isperformed, as illustrated in FIG. 12 .

Subsequently, irradiations with third and subsequent pulses of thepulsed laser light 1 are performed until the depth of the hole 51reaches the thickness of the workpiece W and the through-hole is formed.After each of irradiations with the third and subsequent pulses of thepulsed laser light 1, a heat-affected zone 53 is also produced in amanner similar to the above. As a result of irradiation with the pulsedlaser light 1 a plurality of times, a through-hole 54 is finally formedas illustrated in FIG. 13 . Scanning with the pulsed laser light 1 isthus performed in the cutting direction to form a plurality ofthrough-holes 54 in such a manner that through-holes 54 adjacent to eachother overlap each other, the through-holes 54 adjacent to each othercommunicate each other in the cutting direction, and the workpiece W isthus cut.

In addition, heat-affected zones 53 generated by the heat of the carbonfibers Wa, which remain at a high temperature at the bottom part 52 ofthe hole 51 during let-stand periods after irradiation with the pulsedlaser light 1 and before next irradiation with the pulsed laser light 1,the heat being transferred through the carbon fibers Wa, are presentaround the through-holes 54 formed as described above, which degradesthe quality of the cut workpiece W.

The phenomenon described above is a phenomenon unique to the fiberreinforced composite material. For cutting one position on a workpiecemade of a single material in the depth direction by a plurality of timesof processing, the temperature of a bottom part of a hole formed duringthe cutting is equal to or lower than a processing threshold in a mannersimilar to the above. Thus, even when the heat at the bottom part of thehole is transferred to a region around the hole, the region around thehole is not processed.

In contrast, in the laser processing apparatus 100 according to thefirst embodiment described above, cutting is performed by pulsed laserhaving energy capable of forming a through-hole extending through theworkpiece W in the thickness direction by a single irradiation of thepulsed laser light 1. This can eliminate the phenomenon of transfer ofheat of the carbon fibers Wa, which remain at a high temperature at thebottom part 52 of the hole 51 during the let-stand period describedabove, through the carbon fibers Wa, and prevent generation of theheat-affected zones 53. Thus, in the laser processing apparatus 100according to the first embodiment described above, no heat accumulatedin the carbon fibers Wa remaining at a bottom part of a hole formedduring cutting is transferred to the resin Wb around the hole throughthe carbon fibers Wa, which prevents the resin Wb having a processingthreshold lower than that of the carbon fibers Wa from being heated andthus prevents generation of heat-affected zones 53. As a result, thermaleffects of the workpiece W on the resin Wb during laser processing ofthe workpiece W can be reduced, which prevents degradation in themechanical strength properties of the cut workpiece W caused by cutting,and enables cutting with high quality.

In addition, in the laser processing apparatus 100, the number of timesof scanning with the pulsed laser light 1 for cutting is one, whichresults in a short cutting time. Thus, the laser processing apparatus100 enables laser cutting of a workpiece W with high quality and highefficiency.

To reduce generation of a heat-affected zone 53 during a let-standperiod after the first irradiation with the pulsed laser light 1 andbefore the second irradiation with the pulsed laser light 1 describedabove, the quantity of heat accumulated at the bottom part 52 of thehole 51 may be reduced by performing scanning with the pulsed laserlight 1 by using a galvanometer scanner, for example, and setting ascanning time interval of 100 ms or longer before next irradiation withthe pulsed laser light 1.

As the scanning rate of the pulsed laser light 1 is higher, however, theprocessing depth of a hole formed per a single irradiation with thepulsed laser light 1 is smaller, the number of times of irradiation withthe pulsed laser light 1 needs to be significantly increased, whichincreases the processing time.

In addition, when a processing area of the workpiece W is large, thelaser processing apparatus 100 has no downtime if another processingpoint on the workpiece W is processed during the scanning time intervalof the pulsed laser light 1. In a case where a galvanometer scanner isused, however, the processing area is as small as about 100 mm, andother points on the workpiece W cannot be continuously processed.

Assume, for example, a case where a hole having a diameter of 9.5 mm anda circumference of 30 mm is processed. For example, when the scanningrate v of the pulsed laser light 1 is 6 m/s and the downtime is 300 ms,the scanning time is 30 mm/6 m/s×20 times=100 ms, which is relativelyshort, even if the number of times of irradiation with the pulsed laserlight 1 is 20. In the meantime, the downtime is 300 ms×20 times=6000 ms.Thus, the whole processing time, which is a sum of the scanning time andthe downtime is 6.1 s. The processing speed obtained by conversion ofthe processing time is 0.3 m/min, which is a laser processing speedlower than the speed of laser processing of a typical CFRP.

The laser oscillator 11 used in the laser processing apparatus 100according to the first embodiment is preferably a CO₂ laser oscillator.Thus, for the pulsed laser light 1 used in the laser processingapparatus 100, CO₂ laser light produced by oscillation of a CO₂ laseroscillator is suitable. For example, laser light produced by oscillationof a fiber laser is not absorbed by resin. Thus, in a case where laserlight produced by oscillation of a fiber laser is used, resin isthermally removed by heat transferred from carbon fibers to the resin.In contrast, CO₂ laser light is absorbed by resin at a higher rate thanlaser light produced by oscillation of a fiber laser, and thus enablesprocessing of a through-hole in a shorter time because the heat transfertime is unnecessary and with a smaller quantity of input heat. Thus, useof CO₂ laser light in the laser processing apparatus 100 enables cuttingwith higher efficiency and smaller thermal effects.

Next, differences between the laser processing method using the pulsedlaser as described above performed by the laser processing apparatus 100according to the first embodiment and the laser processing method usinga continuous wave (CW) laser that continuously emits laser light will beexplained. FIG. 14 is a graph illustrating an output waveform of a CWlaser in a case where cutting is performed by the CW laser at the sameprocessing speed as the pulsed laser having the output waveformillustrated in FIG. 5 . The same processing speed means that an averageoutput of the pulsed laser having the output waveform illustrated inFIG. 5 is equal to that of the CW laser having the output waveformillustrated in FIG. 14 .

Note that, as illustrated in FIG. 14 , the CW laser output is lower thanthe pulsed laser output illustrated in FIG. 5 . In addition, asillustrated in FIGS. 14 and 5 , a processing time Twc required forprocessing of one through-hole extending through the workpiece W in thethickness direction in performing cutting using a CW laser issignificantly longer than the processing time Tp required for processingof one through-hole extending through the workpiece W in the thicknessdirection in performing cutting using a pulsed laser. In addition, theprocessing time Twc is equal to the time 1/f from an end of processingof one through-hole to a start of processing of a second through-hole inperforming cutting using a pulsed laser. Thus, the time required forprocessing of one through-hole extending through the workpiece W in thethickness direction is longer for processing using a CW laser than forprocessing using a pulsed laser.

Because a bottom part of a hole irradiated with a laser in the processof formation of a through-hole is immediately below the portion wherethe workpiece W is removed, the bottom part is close to the processingthreshold, has a temperature that is approximately the melting point,which is about 3500° C. regardless of the laser output. In a case wherea CW laser is used, the time during which a bottom part of a hole ispresent in the process of formation of a through-hole is approximated tothe processing time Twc. In a case where a pulsed laser (w) is used, thetime during which a bottom part of a hole is present in the process offormation of a through-hole is approximated to the processing time Tp.

In addition, in the case where the pulsed laser (w) is used, because thetime during which a bottom part of a hole is present in the process offormation of a through-hole is shorter than that in the case where theCW laser is used, the heat transfer from the bottom part of the hole tothe vicinity of the hole can be reduced and the thermal effects on theresin Wb around the hole can be reduced accordingly.

In particular, the processing time Twc required for processing of onethrough-hole by using the CW laser is Twc=1/f={d(1−ro)}/v. Thus, becausethe processing time Twc is longer as the scanning rate v is lower, theprocessing quality is lower as the scanning rate v is lower even whenthe laser output is small.

In contrast, with the laser processing method according to the firstembodiment using the pulsed laser, because the processing time Tprequired for processing of one through-hole does not depend on thescanning rate v, good cutting quality can be achieved even with a lowscanning rate v.

Next, a pulse width in the laser processing method according to thefirst embodiment using the pulsed laser as described above will beexplained. As described above, in the laser processing method accordingto the first embodiment, the time during which a bottom part of a holeis present in the process of formation of a through-hole is approximatedto the processing time Tp. Thus, the pulse width of the pulsed laser ofthe pulsed laser light 1 in the laser processing method according to thefirst embodiment is preferably as short as possible. In addition, aspresented in a specific example described later, when the pulse width ofthe pulsed laser light 1 is equal to or larger than 1 ms, theheat-affected zone 53 is large. Thus, the pulse width of the pulsedlaser light 1 is preferably smaller than 1 ms.

In addition, when a peak output of the pulsed laser light 1 exceeds 150Kw, a phenomenon, called air breakdown, of the atmosphere being changedinto plasma occurs. The atmosphere changed into plasma absorbs andscatters the pulsed laser light 1, which degrades the cutting quality.As will be described later, a minimum required pulse energy for forminga through-hole by a single pulse of the pulsed laser light 1 through aworkpiece made of a CFRP with a polyacrylonitrile (PAN)-based carbonfiber content of 70% and a thickness of 1 mm is 0.15 J. The pulse widthis calculated to be 0.15/150000=1e⁻⁶[s]=1[μs]. Thus, although the pulsewidth is preferably as short as possible, cutting can be performedwithout degrading the cutting quality by setting the lower limit of thepulse width of the pulsed laser light 1 to 1 μs.

It is known that a fiber reinforced composite material can be cut withhigh processing quality by setting the pulse width of the pulsed laserlight to an order of picosecond smaller than nanosecond. In this case,however, the output of the laser oscillator is as low as about 10 W,which results in a very long processing time.

As described above, in the laser processing method according to thefirst embodiment, because the overlap ratio ro is set smaller than 0.5,a plurality of processing holes 41 formed along the cutting direction ofthe workpiece W each have a small opening at a boundary with an adjacentprocessing hole 41. In addition, the bottom part of a hole is closeduntil the hole penetrates the workpiece W in the process of formation ofa processing hole 41. Thus, until a hole penetrates the workpiece W inthe process of formation of a processing hole 41, an exit from the holefor a decomposition product 30 generated during cutting is only presentin an upward direction toward the side of the pulsed laser light 1radiation, that is, toward the processing head 13 in the axial directionof the optical axis 1 a of the pulsed laser light 1. The decompositionproduct 30 is therefore intensely blown upward from the inside of thehole toward the side of the pulsed laser light 1 radiation.

In particular, because the processing threshold of carbon fibers ishigher than that of glass fibers as illustrated in FIG. 4 and carbonfibers need to be processed by a pulsed laser with high pulse energy, ajet of the decomposition product 30 out of the hole is very intense.

In addition, in a case where a recent laser oscillator that generates ahigh peak power is used and the pulse width is set smaller than 1 ms inorder to reduce the thermal effects on a workpiece during cutting, adecomposition product is intensely ejected from a hole in the process offormation of a through-hole. According to experiments conducted by theinventors, in a case where cutting of a workpiece W is performed withuse of a laser oscillator that generates a high peak power and with apulse width set smaller than 1 ms, the ejecting rate of a decompositionproduct 30 from a hole in the process of formation of a through-hole isfound to reach as high as 100 m/s. The peak power is defined as pulseenergy (J)=pulse width (s)×peak power (W).

In addition, as shown by formula (4) described above, the hole diameterd1 of the bottom part 52 of a hole in the process of formation of athrough-hole is preferably small in order to reduce the thermal effectson the resin Wb during cutting. This is also applicable to cutting bythe laser processing method for processing a workpiece W according tothe first embodiment, and the hole diameter of a through-hole formed bythe pulsed laser light 1 is preferably small in order to reduce thethermal effects on the resin Wb during irradiation with the pulsed laserlight 1. When the hole diameter of the through-hole is small, however,the hole diameter of a hole in the process of formation of thethrough-hole is also small, and the aspect ratio of the hole is large,which makes the ejecting rate of the decomposition product 30 from thehole high.

In addition, the decomposition product 30 is ejected in the axialdirection of the optical axis 1 a of the pulsed laser light 1. Thus,when cutting is performed in a state in which the decomposition product30 is let stand, the decomposition product 30 absorbs the pulsed laserlight 1 or scatters the pulsed laser light 1, which degrades theprocessing quality and the processing speed.

In the laser processing apparatus 100, the nozzle 15, which is a sideflow nozzle, is therefore used to solve the aforementioned problem.FIGS. 15 and 16 are diagrams explaining advantageous effects of thelaser processing apparatus 100 illustrated in FIG. 1 . FIG. 15 is adiagram illustrating an example in which the nozzle 15, which is a sideflow nozzle for emitting a jet of gas 23 from outside of the opticalaxis 1 a toward the optical axis 1 a, is used in a manner similar to thelaser processing apparatus 100 illustrated in FIG. 2 . FIG. 16 is adiagram illustrating an example in which an axial nozzle 61 for emittinga jet of gas 23 from a direction along the optical axis 1 a toward aprocessing point is used, which is a comparative example typically usedin cutting of a sheet metal.

In the case where the axial nozzle 61 is used, the flow rate of the gas23 is lowered because the bottom of a hole present in the axial flowingdirection of the gas 23 is closed. In addition, because the direction inwhich the gas 23 is ejected and the depth direction of the hole arecoincident with each other, the decomposition product 30 is likely toenter the inside of the axial nozzle 61. Because the cross-sectionalarea of the flow path of the gas 23 is large and the flow rate of thegas 23 is low at portions of the axial nozzle 61 other than a narrowportion at the distal end thereof, the decomposition product havingentered the axial nozzle 61 accumulates inside the nozzle, that is, onthe optical axis, which absorbs laser light and degrades the focusing oflaser light.

In contrast, with the side flow nozzle, because the jet of gas 23 isemitted from outside of the optical axis 1 a toward the optical axis 1 aat the processing point, the direction in which the decompositionproduct 30 is blown is different from the depth direction of the hole.The side flow nozzle provides a speed component perpendicular to theejecting direction of the decomposition product 30, which is the samedirection as the optical axis 1 a, which can change the ejectingdirection of the decomposition product 30 to a direction other than theaxial direction of the optical axis 1 a, efficiently preventaccumulation of the decomposition product 30 on the optical axis 1 a,and prevent a decrease of the processing speed for processing theworkpiece W due to the decomposition product 30 accumulating on theoptical axis 1 a.

In addition, because no obstruction to the flow of the gas 23 is presentin the direction perpendicular to the optical axis 1 a, the flow rate ofthe gas 23 is now lowered, and the direction in which the decompositionproduct 30 is ejected can be efficiently changed to a direction otherthan the axial direction of the optical axis 1 a.

As a result, the laser processing apparatus 100 can prevent degradationin the mechanical strength properties of a workpiece W obtained bycutting and efficiently perform cutting of the workpiece W, and canperform laser cutting of the workpiece W with high quality and highefficiency in a short time.

In cutting of a workpiece W by the laser processing apparatus 100according to the first embodiment, unlike typical laser cutting, theside flow nozzle described above is used in view of the fact that thedirection in which the decomposition product 30 is ejected is coincidentwith the optical axis 1 a and that a blind hole, which is a hole in theprocess of forming a through-hole is an obstruction to the flow of thegas 23.

The type of the gas 23 is not particularly limited because the purposethereof is to remove the decomposition product 30, and gas such asnitrogen, helium, or oxygen can be used. An application pressure of thegas 23 is preferably 0.1 MPa or higher. When the application pressure ofthe gas 23 is equal to or lower than 0.1 MPa, the effect of removing thedecomposition product 30 may be insufficient, and the processing qualitymay be degraded.

In addition, when a focused beam of the pulsed laser light 1 has acircular profile, the processing hole diameter d of a processing holeprocessed by a single pulse of the pulsed laser light 1 in the cuttingdirection is equal to a kerf width C in laser cutting, that is, a widthof a cut groove in laser cutting. Specifically, when the processing holediameter d is replaced by the focus diameter d of the pulsed laserlight, the focus diameter d is equal to the width of a laser cut groovein laser cutting, and the processing hole diameter d can be replaced bythe kerf width C in formula (3) described above. Thus, when the pulsedlaser light 1 is a circular beam, the kerf width C can be regarded as afocused beam diameter of the pulsed laser light 1. In this case, thewidth of the cut groove in laser cutting can be controlled with highaccuracy by control of the focus diameter d.

Next, a specific example of cutting using the laser processing apparatus100 will be explained. Pulse energy necessary for penetration by asingle pulse was examined using a CFRP with a PAN-based carbon fibercontent of 70% and a thickness of 1 mm as a workpiece, and it was foundout that at least a pulse energy as large as 0.15 J was necessary.

CO₂ laser light was used for the pulsed laser light 1. The focusdiameter of the pulsed laser light 1, that is, the processing holediameter d of a processing hole processed by a single pulse of thepulsed laser light 1 is 200 μm. It was confirmed by the experimentsconducted by the inventors that the cutting quality lowers when thepulse width of the pulsed laser light 1 exceeds 1 ms. Thus, the pulsewidth of the pulsed laser light 1 is preferably smaller than 1 ms.

FIG. 17 is a table illustrating an example of cutting conditions withwhich a good processing quality of a workpiece was obtained by cuttingusing the laser processing apparatus 100. FIG. 18 illustrates an imageof a processing sample cut by the cutting using the laser processingapparatus 100. FIG. 18 illustrates a sample cut by a single scanning ofa workpiece having a thickness of 1 mm with the pulsed laser light 1 ata processing speed of 6 m/min. FIG. 19 illustrates an enlarged image ofa region A of the processing sample illustrated in FIG. 18 .

As illustrated in FIG. 17 , cutting was performed on two processingsamples, which are a processing sample having a thickness of 1 mm and asample having a thickness of 2 mm. As a result, regarding the processingsample having a thickness of 1 mm, the overlap ratio ro was 23%, and thelength h of the heat-affected zone was a small value of 0.1 mm.Regarding the processing sample having a thickness of 2 mm, the overlapratio ro was 29%, and the length h of the heat-affected zone was a smallvalue equal to or smaller than 0.15 mm. Note that, in FIG. 17 , theoverlap ratio ro is expressed in percentage. In addition, it was thusfound out that even when cutting was performed under a low speedcondition of a processing speed of 0.2 m/min, the length h of theheat-affected zone was a small value equal to or smaller than 0.15 mm asa result of setting the frequency of the pulsed laser light 1 to a lowfrequency, and good processing can be performed.

When cutting of a workpiece by using a three-dimensional robot isassumed, processing conditions of low speeds at acceleration anddeceleration and at a corner portion of a cutting path are required. Itis known that processing of the CFRP at low speeds significantly growsthe thermal effects even when the laser output is decreased.

In contrast, the results of the experiments show that the laserprocessing method according to the first embodiment can achieveprocessing with high quality and small thermal effects on the resin ofthe CFRP by performing cutting of the CFRP by changing the pulsefrequency depending on the processing speed.

The laser processing method according to the first embodiment isapplicable to processing of various fiber reinforced composite materialssuch as a fiber reinforced composite material in which a plurality ofreinforcing fibers are incorporated in a single layer along a singledirection, a fiber reinforced composite material in which a plurality ofreinforcing fibers are incorporated in a plurality of layers alongdifferent directions, and a fiber reinforced resin in which shortreinforcing fibers are incorporated randomly in a single layer or aplurality of layers. In this case as well, the advantageous effects ofthe laser processing method according to the first embodiment can beproduced.

In addition, while the reinforcing fibers are carbon in the firstembodiment, the reinforcing fibers may be SiC, B, or the like, and thebase material may be thermoplastic resin typified by polyamide resin andpolycarbonate resin.

In addition, the laser processing method according to the firstembodiment can be applied to processing such as cutting, drilling, andtrimming of a reinforcing fiber composite material, which enablesprocessing to be performed in a shorter time and more efficiently thanmachining and water-jet machining.

As described above, according to the laser processing apparatus and thelaser processing method according to the first embodiment, a workpiece Wcan be penetrated in the thickness direction by a single pulse of thepulsed laser light 1, and thus generation of the heat-affected zone 53caused by a state in which a bottom part of a hole in the process offormation of a through-hole remains at a high temperature can beprevented.

In addition, according to the laser processing apparatus and the laserprocessing method according to the first embodiment, processing isperformed while the gas 23 is applied from outside of the optical axis 1a toward a processing point, which can remove the decomposition product30 to outside of the optical axis 1 a, and prevent a decrease in theprocessing speed of processing the workpiece W caused by thedecomposition product 30 accumulating on the optical axis 1 a.

In addition, according to the laser processing apparatus and the laserprocessing method according to the first embodiment, processing isperformed with the pulsed laser light 1 having a small pulse widthsmaller than 1 ms, which enables cutting of a reinforcing fibercomposite material with small thermal effects on the vicinity of athrough-hole that is formed and with high quality.

Thus, the first embodiment produces advantageous effects of enablinglaser processing of a fiber reinforced composite material while reducingthermal effects on the resin in the fiber reinforced composite material,and being capable of improving the processing speed and the processingquality of a fiber reinforced composite material in laser processing.

Second Embodiment

While an example in which the cut length L is cut by a single scanningwith the pulsed laser light 1 is presented in the first embodimentdescribed above, the cut length L may be cut by scanning with the pulsedlaser light 1 twice. FIG. 20 is a diagram illustrating a laserprocessing method for cutting the cut length L by performing scanningwith the pulsed laser light 1 twice in the laser processing apparatus100 illustrated in FIG. 1 , in which a state of first scanning with thepulsed laser light 1 is illustrated. FIG. 21 is a diagram illustratingthe laser processing method for cutting the cut length L by performingscanning with the pulsed laser light 1 twice in the laser processingapparatus 100 illustrated in FIG. 1 , in which a state of secondscanning with the pulsed laser light 1 is illustrated.

As illustrated in FIG. 20 , the first scanning with the pulsed laserlight 1 processes processing holes 41 a, which are odd-numberedprocessing holes 41. Subsequently, as illustrated in FIG. 21 , thesecond scanning with the pulsed laser light 1 processes processing holes41 b, which are even-numbered processing holes 41, and cuts the cutlength L.

In the second embodiment as well, the control unit 18 controls to changethe relative positions of the processing head 13 and the workpiece W bycontrolling the driving unit 14 to meet the condition of formula (3)above. The control unit 18 also performs control to form the processingholes 41 a by the first scanning with the pulsed laser light 1. Thecontrol unit 18 also performs control to form the processing holes 41 bby the second scanning with the pulsed laser light 1.

The laser processing method according to the second embodiment describedabove can produce advantageous effects similar to those of the firstembodiment described above, and thus produces advantageous effects ofenabling laser processing of a fiber reinforced composite material whilereducing thermal effects on the resin in the fiber reinforced compositematerial, and being capable of improving the processing speed and theprocessing quality of a fiber reinforced composite material in laserprocessing.

FIG. 22 is a diagram illustrating a hardware configuration forimplementing the functions of the control unit 18 illustrated in FIG. 1. As illustrated in FIG. 22 , the functions of the control unit 18 ofthe laser processing apparatus 100 are implemented by a control deviceincluding a central processing unit (CPU) 201, a memory 202, a storagedevice 203, a display device 204, and an input device 205. The functionsperformed by the control unit 18 are implemented by software, firmware,or a combination of software and firmware. The software or firmware isdescribed in the form of computer programs and stored in the storagedevice 203. The CPU 201 implements the functions of the control unit 18by reading the software or firmware stored in the storage device 203into the memory 202 and executing the software or firmware. Thus, acomputer system includes the storage device 203 for storing programs,which, when the functions of the control unit 18 are executed by the CPU201, results in execution of steps of performing the operation of thecontrol unit 18 described in the first embodiment. In other words, theprograms cause a computer to execute the processes performed by thefunctions of the control unit 18. The memory 202 is a volatile storagearea such as a random access memory (RAM). The storage device 203 is anonvolatile or volatile semiconductor memory such as a read only memory(ROM) or a flash memory, or a magnetic disk. Specific examples of thedisplay device 204 include a monitor and a display. Specific examples ofthe input device 205 include a keyboard, a mouse, and a touch panel.

The configurations presented in the embodiments above are examples ofthe present invention, and technologies of the embodiments can becombined with each other or with other known technologies, or can bepartly omitted or modified without departing from the scope of thepresent invention.

REFERENCE SIGNS LIST

1 pulsed laser light; 1 a optical axis; 2 condenser lens; 11 laseroscillator; 12 optical path; 13 processing head; 14 driving unit; 15nozzle; 16 nozzle moving mechanism; 17 detecting unit; 18 control unit;21 condenser lens; 22 optical unit; 23 gas; 28 offcut; 29 processedproduct; 30 decomposition product; 41, 41 a, 41 b processing hole; 42processing region; 51 hole; 52 bottom part; 53 heat-affected zone; 54through-hole; 61 axial nozzle; 100 laser processing apparatus; 201 CPU;202 memory; 203 storage device; 204 display device; 205 input device; Ckerf width; d processing hole diameter; d1 hole diameter; f frequency; Lcut length; N number of pulses; ro overlap ratio; Tp, Twc processingtime; v scanning rate; W workpiece; Wa carbon fiber; Wb resin.

The invention claimed is:
 1. A laser processing method for laserprocessing of a workpiece made of a base material and a fiber reinforcedcomposite material, the fiber reinforced composite material containingfibers having a thermal conductivity and a processing threshold higherthan physical properties of glass fibers, the laser processing methodcomprising: processing the workpiece by forming a plurality ofthrough-holes extending through the workpiece by irradiating theworkpiece with pulsed laser light from a processing head whilerelatively moving the workpiece and the processing head in apredetermined cutting direction, wherein the pulsed laser light has apulse width smaller than 1 ms, a focus diameter d being equal to or lessthan 200 μm, a pulse energy being equal to or larger than 0.5 J, and anenergy density capable of forming each of the through-holes by a singlepulse, and each of the through-holes is formed by a single irradiationwith the pulsed laser light, wherein during the laser processing, a jetof gas is emitted from outside of an optical axis of the pulsed laserlight toward the optical axis, and an overlap ratio ro being a ratio ofa length by which two of the through-holes adjacent to each other in thecutting direction overlap each other in the cutting direction to thefocus diameter d meets a predetermined range, wherein the workpiece isprocessed by changing a pulse frequency of the pulsed laser lightdepending on a processing speed of the workpiece in such a manner that arange of the pulse frequency is depending on a range of the processingspeed, the range of the pulse frequency being equal to or larger than 21Hz and equal to or less than 700 Hz while the range of the processingspeed being equal to or larger than 0.2 m/min and equal to or less than6 m/min, wherein the jet of gas is emitted from the side of a processedproduct toward a processing point of the workpiece.
 2. The laserprocessing method according to claim 1, wherein when the focus diameterd represents a focus diameter of the pulsed laser light in the cuttingdirection, a processing length is represented by a processing length L,and the number of pulses of the pulsed laser light emitted to aprocessing region having the processing length L is represented by thenumber N of pulses, the predetermined range is expressed by thefollowing formula (1):0<ro=(d−L/N)/d<0.5  (1).
 3. The laser processing method according toclaim 2, wherein the pulsed laser light is focused into a circular shapeand emitted to the workpiece, and the focus diameter d is equal to awidth of a laser cut groove cut by the pulsed laser light.
 4. The laserprocessing method according to claim 2, wherein the overlap ratio ro is0.2.
 5. The laser processing method according to claim 1, wherein alaser oscillator to emit the pulsed laser light is a CO₂ laser.
 6. Thelaser processing method according to claim 1, wherein during the laserprocessing, the jet of gas is emitted with an application pressure of0.1 MPa or higher.